Oak savanna restoration project underway at Horseshoe Bend

Dickinson County Conservation Board vegetation specialist Aric Ping takes readers this week through a fantastic oak savanna restoration process started this summer at Horseshoe Bend Wildlife Area.

If you’ve ever gone through our parks and wondered, “Why did they cut down that tree?” or, “Why did they burn this area?” then this is the post for you. The goal of this post is to inform readers on the “whys” and “hows” of ecological stewardship and restoration projects taking place on Dickinson County Conservation Board properties. I’ll start by giving a general overview of what we do and why and then show how that process is guiding one of our current projects.

(Identifying the leaves of trees native to northwest Iowa.)

Generally, our main goal on our properties is to increase bio-diversity. Here in northwest Iowa, that means restoring land to native tallgrass prairie, wetlands, or oak savanna and returning natural processes to these ecosystems in the hopes of creating as many habitat opportunities for wildlife as possible.

How we go about our restoration varies from site to site. Each site has different characteristics. They have different topography, hydrology, and vegetation, but one of the biggest factors that guides our management is historical site use. Strategies for restoring tallgrass prairie from scratch on a former row-crop field, for example, are entirely different from the strategies used for rejuvenating a wetland remnant site that has been heavily grazed. Most of our sites have had several different uses over the years, further complicating restoration. The site that best epitomizes the complexities of our stewardship practices is Horseshoe Bend.

Horseshoe Bend is home to fragments of tallgrass prairie, wetlands, river bottom forest, and oak savanna – a unique mixture of ecosystems for an area of less than 200 acres. The site has been used through its history for row-crop fields, grazing, crop tree production, and game animal management. Each of these practices have changed the park in different ways, but the one thing they all have in common is that they have skewed the balance of plant competition in favor of non-natives.

The areas that were row crops were tilled and have no remaining native perennials. The areas that were grazed are dominated by monocultures of invasive smooth brome and reed canary grass, while only the hardiest of natives cling on to the fringes. Crop tree production areas and game animal shelterbelts have shaded out grasses of any sort, providing a fire-proof harbor for shade-tolerant invasive trees such as buckthorn and bush honeysuckle.

Over the long term, all of these areas at Horseshoe Bend will be restored to diverse stands of native vegetation, but our first priority is restoring the rarest and most diverse of these ecosystems, the oak savanna.

Oak savannas are extremely productive ecosystems that provide a wide range of habitat and resource opportunities for wildlife. They contain areas that receive full sun, areas that are completely shaded, and everything in-between. As a result, a healthy oak savanna will typically contain a full spectrum of full-sun to full-shade plant species, and a greater variety of insects and animals than forests or even prairies. This wealth of biodiversity is predicated on the balance between shade and sun, and that balance is maintained by fire.

Fire in an oak savanna is a feedback loop. Fires suppress woody undergrowth from dominating below the canopy, which allows a healthy mix of fire-adapted grasses and forbs (wildflowers) to flourish. These grasses and forbs in-turn readily carry fire, which further suppresses woody undergrowth, which again promotes grasses and forbs that carry fire, and so on. Oaks themselves, especially bur oaks, are well-suited for fires. Their thick bark protects them from the heat, they are great at compartmentalizing the damage that does occur, and their fallen leaves are excellent for carrying fire.

The south side of Horseshoe Bend has approximately 5 acres of remnant oaks, but long-term fire suppression has skewed the balance of sun and shade, allowing invasive shade-tolerant plants (buckthorn and bush honeysuckle) to shade out the native grasses and forbs, which eventually eliminated the ability of the savanna to carry fire. This process ultimately changed the oak savanna into a weedy woodland that we are now returning to savanna.

The process began in earnest in July, when the remnant oaks were discovered during a vegetation survey. We then referenced historical aerial photography to confirm the presence of savanna in the past.

Aerial photo of Horseshoe Bend Wildlife Area in 1939

1939 photo courtesy of Iowa Department of Natural Resources Aerial Photo Project

Aerial satellite image of Horseshoe Bend Wildlife Area

2013 photo courtesy of Google Maps

The two above photographs show a comparison of Horseshoe Bend in 1939 and 2013. As you can see, there were a lot fewer trees in 1939, even after decades of fire suppression.

From there, a restoration timeline was developed and invasive and weedy trees began to be removed in August. The project is ahead of schedule as the purchase of a skid loader has sped up restoration. The next step will be to reseed the area back to native oak savanna species. The area will begin to resemble a savanna within a year with restoration work being complete in 3-5 years.

More projects are in the works, and you will continue to see positive changes in our parks over time as we carry out our restoration efforts and push plant competition back in favor of native species.”

Photo of native prairie flowers

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